Cheap PCB fab place (for non-urgent stuff)
in [Design]
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From: Joerg on 17 Apr 2010 12:02 krw(a)att.bizzzzzzzzzzzz wrote: > On Sat, 17 Apr 2010 07:12:00 -0700, Joerg <invalid(a)invalid.invalid> wrote: > >> Nico Coesel wrote: >>> Joerg <invalid(a)invalid.invalid> wrote: >>> >>>> Joel Koltner wrote: >> [...] >> ... (Especially >>>>> for commercial products -- for the military/NASA/etc. where price is no >>>>> object, I expect niche "leaded" assemblers will stick around... just as >>>>> there's already a niche market in de-balling lead-free BGAs and >>>>> re-balling them with leaded solder, often at a cost close to or >>>>> exceeding the original price of the part!) >>>>> >>>> BGA is another story. I avoid them when at all possible because they are >>>> causing so much grief. Having a stiff ceramic-like chip with solder pads >>>> on a structure such as FR-4 that is by nature somewhat flexible has >>>> IMHO always been a rather sick concept. >>> AFAIK BGAs are based on an FR4-ish laminate so it can bend along with >>> the PCB. In my experience some assembly houses do not master their >>> soldering process and some PCBs are difficult to solder because the >>> heat absorbtion is not evenly distributed (hot spots/cold spots). If a >>> BGA package is causing problems its usually not the package itself but >>> the PCB or the assembly house. >>> >> The failures I've heard about were in mass products which are definitely >> professionally soldered. The BGAs I've seen were some sort of ceramic. >> After all, a die cannot bend. Even if it was FR-4, think about it, what >> will happen if two circuit boards soldered together via bumps are bent? >> >> Same goes for larger DFN packages but often one doesn't have a choice. I >> will always prefer MSOP or anything with pins because there is some >> movement compliance in the pins. > > We don't like Q/DFNs because they're harder reflow reliably, particularly with > RoHS solder. BGAs above .8mm, OTOH, are simple so we use them whenever > possible. There is rarely a choice between packages this diverse though. > Unfortunately the SSOP versions of some of my favorite chips are out of stock very often while there's always some DFN on the shelf. No idea why people seem to prefer them, maybe because they use a smidgen less real estate. It's like with chocolate, my wife craves noisette cream chocolates but they only have all the others on the shelf. Life's like a box of ... wait, didn't Forrest Gump's mom say that? -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: krw on 17 Apr 2010 14:04
On Sat, 17 Apr 2010 09:02:08 -0700, Joerg <invalid(a)invalid.invalid> wrote: >krw(a)att.bizzzzzzzzzzzz wrote: >> On Sat, 17 Apr 2010 07:12:00 -0700, Joerg <invalid(a)invalid.invalid> wrote: >> >>> Nico Coesel wrote: >>>> Joerg <invalid(a)invalid.invalid> wrote: >>>> >>>>> Joel Koltner wrote: >>> [...] >>> ... (Especially >>>>>> for commercial products -- for the military/NASA/etc. where price is no >>>>>> object, I expect niche "leaded" assemblers will stick around... just as >>>>>> there's already a niche market in de-balling lead-free BGAs and >>>>>> re-balling them with leaded solder, often at a cost close to or >>>>>> exceeding the original price of the part!) >>>>>> >>>>> BGA is another story. I avoid them when at all possible because they are >>>>> causing so much grief. Having a stiff ceramic-like chip with solder pads >>>>> on a structure such as FR-4 that is by nature somewhat flexible has >>>>> IMHO always been a rather sick concept. >>>> AFAIK BGAs are based on an FR4-ish laminate so it can bend along with >>>> the PCB. In my experience some assembly houses do not master their >>>> soldering process and some PCBs are difficult to solder because the >>>> heat absorbtion is not evenly distributed (hot spots/cold spots). If a >>>> BGA package is causing problems its usually not the package itself but >>>> the PCB or the assembly house. >>>> >>> The failures I've heard about were in mass products which are definitely >>> professionally soldered. The BGAs I've seen were some sort of ceramic. >>> After all, a die cannot bend. Even if it was FR-4, think about it, what >>> will happen if two circuit boards soldered together via bumps are bent? >>> >>> Same goes for larger DFN packages but often one doesn't have a choice. I >>> will always prefer MSOP or anything with pins because there is some >>> movement compliance in the pins. >> >> We don't like Q/DFNs because they're harder reflow reliably, particularly with >> RoHS solder. BGAs above .8mm, OTOH, are simple so we use them whenever >> possible. There is rarely a choice between packages this diverse though. >> > >Unfortunately the SSOP versions of some of my favorite chips are out of >stock very often while there's always some DFN on the shelf. No idea why >people seem to prefer them, maybe because they use a smidgen less real >estate. Maybe people like the SSOPs, so buy them all. ;-) I guess I never compare availability since we wouldn't think of using a DFN if a SSOP was an alternative. Unfortunately, D/QFNs are all that's available in many regulators and codecs. >It's like with chocolate, my wife craves noisette cream >chocolates but they only have all the others on the shelf. Because they've sold all the good stuff. >Life's like a box of ... wait, didn't Forrest Gump's mom say that? DFNs? No, I don't remember that part. |